Gas‐Permeable Highly Sensitive Nanomesh Humidity Sensor for Continuous Measurement of Skin Humidity

Abstract On‐skin humidity sensors can be used to measure the sweat rate on the human skin surface. However, it is challenging to realize a precise, long‐term skin humidity measurement. The main challenge is to develop an on‐skin humidity sensor that has gas permeability, high sensitivity, and flexibility simultaneously. Porous materials and electrodes can enhance the properties of the humidity sensor for fulfilling continuous monitoring. Herein, a humidity sensor composed of nanomesh Au electrodes and nanomesh humidity‐sensitive materials, is reported. The porous structure makes the sensor flexible and gas permeable, increases the surface area, and leads to high sensitivity. The sensor has a high sensitivity of 640 000% in the relative‐humidity range of over 40–100%, together with a gas permeability similar to that of an open environment. The gas permeability suppresses the skin inflammation, endows natural evaporation of sweat, and brings an identical condition with bare skin. To evaluate the utility of the nanomesh sensor, on‐skin humidity measurements are performed, and the humidity change due to sweating after exercise is recorded.